did you have any luck with just calling? Sometimes they are more flexible if they know that you are already planning on staying but just want to extend your stay. You can also check websites like expedia, orbitz, travelocity, etc as they may have inventory available that the hotel itself doesn't have.

Then I would keep checking every 7-10 days or so and keep inquiring on availability. also if you were able to get one of the other two on property hotels I'm sure they'd be very helpful with transfering your luggage.